Boreal soil homogenization after conversion to agricultural use is constrained by carbon dynamics and soil health

• Farming converted boreal soil led to swift homogenization to agricultural benchmarks. • Accelerated soil respiration was linked to high soil C and low compaction. • Farmed low fertility boreal Podzols may behave like slash and burn agriculture. • Management focused on soil C could regenerate these soils for long-term C storage. As climate changes progress, land use conversion (LUC) intensifies in boreal regions, fuelling concerns that post-LUC farming may cause further decline in soil carbon (C) by altering C pools and degrading soil health. However, detailed data on how boreal soils respond after LUC to agriculture remains scarce. This study addresses this gap by analysing a representative farm in Happy Valley-Goose Bay in Labrador, Canada converted from mixed boreal spruce forest and sphagnum peat bog between 2013 and 2018. C concentrations were measured in a grid pattern across a 0–5 year management chronosequence at two depths (0–15 and 15–30 cm). Time-partitioned burst respiration (24 h intervals) was used to assess the soil’s functional status in relation to changes in background and management-altered physicochemical factors. Respiration patterns closely followed total soil C and nitrogen, and were significantly affected by compaction, indicating that C levels, moderated by hydrology, drive respiration in converted sandy Podzols. Soils shifted toward what might be argued are agricultural norms within five years: higher respiration and pH, and increased uniformity of C/N, phosphorus, aluminium, iron, magnesium, and manganese concentrations. Variability in soil function was most strongly linked to soil C, as high-C soil resisted homogenization but supported vigorous crop growth, while homogenized low-C soil struggled to support plants. This study demonstrates that C loss post-conversion in boreal Podzols is a clear danger to soil fertility in spite of rapid homogenization to agricultural norms.